Electric vehicle and an energy storage power station generally need a power battery with large capacity as the power supply. Except for the large capacity, the power battery should also possess good security and longer cycle lifetime etc., so that to achieve the using standard and meet people's requirements.
In prior art, when the power battery is overcharged, the decomposition of the electrolyte in the power battery will result in that excess heat is generated inside the power battery which may cause fire; or will increase the pressure inside the power battery and lead to explosion. Therefore, before the power battery out of control, an outer short circuit structure is needed to cut the Fuse structure in the main circuit of the power battery, so as to stop the power battery from being charged. For example, when the power battery overcharged, and a certain pressure is generated inside the power battery, the outer short circuit structure works, the power battery itself forms a circuit, so as to fuse the Fuse, and thus the main circuit is cut. The outer short circuit structure works in a certain pressure, its over-current capacity is larger than the Fuse's, which cannot be fused before the Fuse in a high current. FIG. 1 is a structural schematic diagram of a part of the top cover of the power battery in prior art. As shown in FIG. 1, in prior art, a reversing piece 1 is adopted to achieve the function of the outer short circuit structure, the reversing piece 1 adopts a circular disk with uniform thickness, a raised hollow top surface is provided at the center of the circular disk. The reversing piece 1 and the cathode column 2 on the top cover of the power battery are disconnected and insulated when in normal use. When the power battery is overcharged and generates a certain pressure, the pressure will push the reversing piece 1 to move, so that the raised top surface of the reversing piece 1 is connected to a conducting piece 3, the conducting piece 3 is electrically connected with the cathode column 2, so as to form a circuit loop in the power battery, then the Fuse is fused, the main circuit is cut off, which protects the power battery.
However, when the power battery is overcharged and generates a certain pressure, after the pressure pushing the reversing piece 1 to move, the raised top surface of the reversing piece 1 contacts the conducting piece 3, the raised portion is of a hollow structure, the over-current area is small, a high current is generated at the position where the raised portion of the reversing piece 1 contacts the conducting piece 3, when the current is high enough to a certain degree, the reversing piece 1 may be fused, which leads to fire or explosion of the power battery.